8Rubenstein R N. Computational Estimation and Related Mathematical Skills [J]. Journal for Research in Mathematics Education, 1985, 6(2): 106-119.
9Owder J T. Estimation and Related Topics [A]. In: Grouws D A. Handbook of Research in Mathematics Teaching and Learning [C]. NY: Macmillan, 1992.
10Urphy M R. Teaching and Applying Computational Estimation Skills in Grade 8 [J]. (Simon Fraser University (Canada)1989), MAI Winter, 1992, 30(04): 986.
